In order to find ways of prolonging wheel working time and
improving the reliability of their exploitation, it is necessary to know
the general picture of operating conditions for rolling stock, the
circumstances of damage while changing their dynamics, wear resistance,
work refusal and work continuance. Any of damages to the surface of
wheel roll has a negative influence on cutting conditions while
restoring its profile. When determining cutting conditions, it is
necessary to pay attention to the character of damages and their
influence on the repair process ([TEXT NOT REPRODUCIBLE IN ASCII] 1997).

An exception to the exploitation of rolling stock is repair, both
planned and unplanned, usually done by identifying 4 groups of causes:
roll surface wear, defects to the roll surface, rim, wheel flange and
tread, defects to pulley, the central part of the wheels, worn tread in
the central part of the wheel flange and axle half shafts (Mikaliunas
2000; Mikaliunas et al. 2002, 2004; Lingaitis et al. 2004).

Roll surface wear occurs due to related force effect and squash
with ordinary force. The equal wear distribution pump should be
observed. The wear of the profile is not evenly distributed and depends
on the priority of wheel abutment and rail contact condition to run
round which seems to be a helpful tool for avoiding the wear of the
flange. Under such conditions, the wheel passes to compact contact with
the rail and flange wear sharply slows down and takes place when both
flange and the profile of the roll surface wear at the same time; mostly
it gets to condemn the thickness of a wheel pair of flange
'B'. In the vertical flange section, flange wear prevents from
roll surface wear.

Defects to the roll surface may be twofold--caused by wear and
those of thermodynamic origin. All these defects are caused by the whole
complex of reasons, including technological (low steel quality, breach
of processing routine), and are able to make use of 9 wrong types
regulating the gathering momentum of the wheel pair, a wagon position,
its plan and profile etc. (Somov, Bazaras 2007).

The upper metal layer of the roll surface of the axle half shaft
gets into grinding and the whole picture essentially differs from that
of the new wheel. It can be explained by the 'burn' zone that
reveals the presence of both sections--a 'white layer' having
the hardness of 7.0/10.0 GPa and an extremely granulated grain structure
on its surface. Grain size is from 2 to 3 mcm. According to microscopic
electron analysis, microstructure consists of martensite and carbides.
The size of carbide pieces is in the range of 1.0/1.5 mcm.

2. A Technical Review of the Main Reasons for Wheelset Withdrawal
and Analysis of the Dynamics of Wheel Breakage

In a modern wagon park, continuous rolling wheels of freight wagons
are taken out of operation first of all not because of wear but on
account of damage to the wheel roll surface due to local displacements
at wheel-and-rail contact places. The presence of the above-mentioned
defects is the main reason why wheelsets get repaired at traction and
rolling stock maintenance depots (see Table 1).

When wagons are in the planned repair, quite a different picture of
the wheels to be repaired can be observed.

The largest amount of wheels (49.9%) is brought to the depot
because of differences in the diameter of the wheels in a wheelset; 25%
of wheels are processed by limited rolling; 10% of wheels are processed
because of local displacements and 4%--due to slipping caused by fatigue
deformation; the breaks of the hard layer and the fragments of the
exterior side of the rim make up 5.66, 0.03 and 5.8% respectively ([TEXT
NOT REPRODUCIBLE IN ASCII] 1984).

The wheels of the northern-direction train exhibit a higher wear
rate due to the use of brake blocks. The highest percentage of wear
caused defects can be noticed in trains travelling in Trans-Siberian
direction (90.4%) the wheel pairs of which with hard surfacing, slips
and kinks are rarely found.

A higher wear rate of wheel flanges is usually observed in wagons
following the routes full of small radius curves. On these routes, in
case there is an unplanned turning of wheel pairs, flange cutting is the
main factor.

A higher rate of defects to the wheel roll surface is also
evidenced by other sources. The analysis of the dynamics of wheel
breakage over the period of 30-years of exploitation has shown that the
character of occurring failures has essentially changed to the side of
remarkably lower failures due to wear and contact fatigue. At the same
time, the amount of defects that have appeared due to braking has
increased for all types of wagons.

Brake defects make up to 75/90% in uncoupled repair nowadays. Wear
defects make up to 58% and brake defects--15.8% in planned repairs.
Cutting flanges is steadily growing.

In the last ten years, the breakage of exploited wheels has
displayed the following tendencies: the amount of damaged wheelsets with
slips and hard surfacing has remained at the same level; the number of
repairs due to the wear of flanges and sharp run-in has significantly
increased. The growth of wheel fracturing and rim splitting has been
also observed.

As noted above, the proportion of damages to the roll surface of
the wheelset strongly depends on physical and mechanical properties of
steel used for wheels and exploitation conditions for rolling stock. An
increase in wheel quality determines changes in the percentage of
defects, which prevents from wheelset exploitation. An increase in the
strength properties of steel used for wheels has nearly allowed avoiding
defects such as slipping caused by fatigue deformation and those of
thermo mechanical origin.

The Ministry of Transport and Communications of the Republic of
Lithuania in collaboration with institutes and manufacturing industry
carries out complex research on manufacturing wheels that would better
meet the requirements for the prolonged exploitation of wheels.

To increase the contact strength of the wheel roll surface, the
following ways can be recommended: first, an increase in the area of
contact between wheel and rail; second, the use of sturdy elements in a
wheel pair and railroad structures; third, the use of new materials that
would allow high thermal and contact pressure; fourth, improvement to
thermal processing during steel production and restoring the structure
of wheelset steel with the aim at forming rational physical and
mechanical properties in the upper layers of the wheel roll surface.

3. Theoretic and Experimental Research on the Process of High-Speed
Profile Grinding (HSPG)

Today, a grinding process for repairing the profile of the wheel
roll surface is not as widespread as turning or cutting. In the machines
used for grinding the profile of the roll surface, a low cutting level
taking much time is applied. This is the reason why the majority of
machine constructions are created for processing wheelsets with no
wheeling them from under the rail carriage or truck. The low efficiency
of a grinding machine is compensated by the elimination of lifting,
dismantling and assembling, which justifies the above discussed
situation. In addition, there is a possibility of processing a wheel
pair produced by using a mechanical process and possessing a hardened
surface without removing an efficacious metal layer of the rim.

Presently, wheelset grinding is used in the countries that operate
high speed railway lines which means the application of higher
requirements for the precision and quality of processing wheel pairs.

In Osaka, Japan, a grinding machine for the profile of the wheelset
roll surface serves the entire high-speed railway line in New Tokaido.
Wheelset rotation of grinding is made using a 22 kW motor and the
rollers resting on the wheel flange. A peripheral (linear) speed of
wheel rotation is 1000 mm/min and the speed of the feed 0.015+0.15
mm/min.

Grinding the profile of the roll surface is performed on a special
facility that allows processing 4 wheels for one carriage at once
leaving the wheelset under the wagon. It takes 40 minutes to process the
wheels of one carriage.

According to the data source from Japan, since 1965, a machine for
tire grinding has been used on the same railway line in Tokaido. A
rotational speed of leading rolls rotating a wheel pair is 5/15 RPM. A
rotational speed of the grinding circle is 300 RPM with the diameter and
thickness of 845 mm and 96 mm respectively in the beginning.
Notwithstanding higher standards maintained in the manufacture of
wheelsets used in the above mentioned railway line, irregular
granularity due to braking still occurs and usual tiring methods are not
used because of a harder metal used for producing wheels. The capacity
of the facility is 40 wheel pairs (10 wagons) per day.

In the USA, two companies started manufacturing grinding machines
for restoring the profile of the wheel roll surface. The grinding
machine made by the Belt Railway Co guarantees a rotational speed of a
wheel pair reaching 4/5 RPM. A grinding circle of 365 mm in diameter
rotates at about 65 m/s. When the circle wears off, rotational speed
increases and cutting speed is kept unchanging.

Grinding both the wheel roll surface and rim is carried out by
performing circle cuttings. In the grinding machines produced by the
above mentioned company, grinding the wheelsets of diesel locomotives is
performed following the process they are wheeled out. The procedure
takes about 4 hours to process a double axle trolley depending on the
condition of bandages.

The grinding machine manufactured by Withing Corporation is
designed for processing wheelsets with and without wheeling them out of
a locomotive. The profile of the grinding wheel is corrected after
processing every two wheelsets. Therefore, a special correcting facility
is established on the supports. Correction takes 20 minutes. Despite
frequent corrections, it is possible to grind out 200 wheels with one
grinding circle.

The grinding circle of 914 mm in diameter has a fully negative
profile of the bandage. The 40 HP DC motor rotates the wheel at a speed
of about 33 m/s. Processing modes are shown in Table 2.

It is known that grinding is used for repairing wheel bandages of a
tram wagon.

Heavy machinery manufacturer Kramatorian designed a modernized
machine with 4 supporting wheel holders by replacing roughing supports
with grinding stocks. Slants with the gradients of 1:20 and 1:7 are to
be grinded. The speed of the grinding circle was suggested to be kept
constant at [V.sub.i] = 50 m/s; grinding with emulsion was done. The
power of the motor is 46.65 kW. A rotational speed of the circle is
950/1900 rpm and the feed reaches 0.15 rpm (Bhateja 1979).

The company Sculfort Systemes Sonim presented the results of
research on the comparison of the following three methods for secondary
grinding of a wheelset: grinding, milling and turning. This enabled
French National Railway Corporation SNCF (Societe Nationale des Chemins
de Fer Francais) to decide on choosing processing by turning on a
digitally controlled machine with a wear-resistant tool made from the
titan-carbide layer. According to SNCF, the secondary shaping of the
wheel using a cutting tool under equal conditions is 4 times less
expensive than shaping using a grinding circle. Thus, they rejected
processing by milling at the first stage of research. The company did
not research the process of high-speed grinding because they considered
the possibility of using the above-mentioned methods for repairing
high-speed equipment when the quantity of metal removed from the wheel
rim was not large.

The above-mentioned cases show that the level of cutting modes used
for the existing technology for grinding the wheelset roll surface is
not high. Presently, a qualitatively different grinding method for steel
forge roughing is used both in our country and abroad. This technique,
initially named as a power and high-speed method in Russia, as a
high-efficiency method in the USA and as an integral method in Germany,
ensures the best effectiveness and manufacturing output when a large
amount of metal is removed. The method replaces turning, milling and
shaving with the removal of a large amount of chips. At present, in
foreign countries, machines for round grinding of up to 2000 mm3/mm
capacity are operated.

In other countries, this process found its place in metal factories
and is used for roughing rolled stock, which also guarantees the removal
of metal up to 12.7 mm in one pass with no loss of precision. It should
be mentioned that the above introduced method of high-speed grinding
became widely used in the field of shaping surfaces.

In grinding shaped surfaces applying the cutting method, certain
machines cut as deep as 50 mm and the grinded outline is 300 mm wide.
The power consumed during this process is 110 kW. High-speed grinding,
as a new technology, became realizable with the invention of new
high-speed abrasive circles, rigid and vibration-resistant grinding
machines and by using more reliable safeguards for grinding circles.

The analysis of methods used for mechanical processing of the
wheelset showed that the high-speed profile grinding (HSPG) process
method was the most preferable one in the restoration of the roll
profile of the repaired wheelset. The analysis of cost effectiveness has
also indicated that the best way for restoring the wheelset roll surface
is using a specialized high-efficiency grinding machine. The available
results led to making a proposal on designing an experimental grinding
machine for re-establishing the wheelset roll surface using the HSPG
method.

HSPG is characterized by a high cutting mode level and the maximum
summed length of all cutting blades working simultaneously. A high level
of the cutting mode is achieved using a high speed of cutting (80 m/s
and above) and cutting feed (10 mm/min and above). The maximum summed
length of all cutting blades working simultaneously was received using a
shaped profile and the most abrasive circle known today.

As far as the kinematical scheme is concerned, HSPG does not differ
from an ordinary cutting-based grinding process; however, the progress
of its physical and mechanical processes distinguishes itself by many
important peculiarities. Research on these processes was not
sufficiently reviewed. Instead, experimental and theoretical research on
the HSPG process of producing wheel steel was done.

Theoretical research on the parameters of the HSPG process using
the methods proposed by Prof. S. S. Silin ([TEXT NOT REPRODUCIBLE IN
ASCII]) was carried out.

The balance of mechanical and heat energy is determined by the
following basic equation:

Heat transferred from the grinding zone to the detail, circle and
chip:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (4)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (6)

The influence of the cutting mode on heat quantity transferred from
the cutting zone to the detail, circle and chip respectively is shown in
Figs 1 and 2. The analysis of formulas (1/6) and Figs 1 and 2 shows that
heat quantity transferred to the detail and circle increases with an
increase in detail speed and grinding depth.

Dimensionless complexes K, M, Z/[D.sub.c], L, [D.sub.c]/d are
calculated as outgoing from known information. Considering an allowable
wear of a high capacity circle, we determine a rotational speed of the
detail (wheelset) to be [v.sub.d] = 190 m/min when cutting feed is 11.8
mm/min.

4. Thermal Processing of the Wheel Profile

During the process of manufacturing a primary wheel and bandage,
the upper layer hardness of 260/310 HB is reached in a pulsating
hardening way after preheating in the furnace. In the depth of 30 mm,
metal hardness usually does not exceed 265 HB because of low heat
penetration into metal and bandage. That is why the entire hardened
metal layer gets fully removed already within the first two subsequent
repairs. During all remaining time, the wheel and bandage are exploited
almost without the hardened metal layer; thus, they wear off sooner and
defects to contact fatigue appear. Wheels are repaired more frequently,
and therefore a useful wheel metal layer is taken off as a chip in the
grinding process. When using modern wheels and bandages, a requirement
that the metal layer of the run must be of 290/300 HB hardness should be
satisfied. The same hardness must be kept through all depth necessary to
be present through the whole exploitation of the wheel. While restoring
a wheelset and shaping the wheel roll surface, in order to efficiently
use metal, it is not purposeful to grind a part of the metal layer
turning it into shaving. There are known wheel regenerating methods when
the upper metal layer is repeatedly annealed to the hardened pearlite
with its subsequent grinding.

However, these methods do not ensure physical and mechanical
properties of metal used for the wheel roll surface important for
improving wheel durability. The main purpose of these methods is to
increase the productivity of the grinding process and to decrease the
use of the hardened layer (Somov, Bazaras 2006; Bazaras, Somov 2009).

The wheel restoration method, by which the wheel roll surface is
first processed employing polishing and grinding in order to restore
physical and mechanical properties of rim metal, is the void of similar
defects. The estimation of the quality of all wheel restoration methods
revealed that this method among other assessed methods, according to the
classification scheme established by the experts, had the best special
quality indices accounting for: its usage in other application fields
(P1), the thermal processing of the wheel up to 600 HB (P2) and that of
up to 320 HB (P3), the efficient processing of wheels with defects to
run surface (P4), physical and mechanical properties of rim metal
regeneration (P5), the structural simplicity of a cutting tool (P6), the
tool fixing and regulating complexity (P7), the formation of comfortable
and easy-to-remove shaving (P8) and the necessity of subsequent shaving
processing (P9). As a result, this method possesses the highest value of
the general quality index (Q). According to the results of the analysis
regarding the effectiveness of restoration methods (Bazaras, Somov
2009), this method seems to be the most acceptable one.

The method that is the most similar to the one discussed above in
terms of technical essence and achievable results, is the restoration of
the wheel roll surface of railway rolling stock.

The essence of this method is that annealing and sudden cooling of
the upper metal layer is done before mechanical processing.
Consequently, the metal surface becomes sorbitic pearlite or sorbite of
290/320 HB hardness in the depth of 8 mm from the roll surface. After
thermal processing, processing the mechanical surface using grinding is
done, during which a metal layer of 3+4 mm with damages or defects is
taken off.

However, this method does not ensure the thermally processed metal
layer to be equal to the whole depth of the wheel roll surface profile.
This happens because of a complicated way of making the gap between the
inductor and the worn wheel roll surface being equal. The gap can vary
in the range of e = 3/15 mm, depending on the characteristics and
diameter of the wheel (Fig. 3). Variations in the gap value result in
variations in the inductivity of the system
'transformer-inductor-wheel', and hence, in the resonant
frequency of the contour, which results in changes in cos [phi] and
power used by the generator. An increment in the gap decreases power,
which means it is not fully used. In addition, the depth of annealing
decreases and the system does not work properly. To improve the
stability of the system, a separate generator should be connected to
every inductor (heating head). Even if the rolled layer of the wheel
roll surface is less than 3 mm at some spots of the profile, metal may
not attain necessary strength or thermal processing may not occur at the
necessary depth of 8 mm. Moreover, thermal processing reaches its
maximum depth not on the wheel roll surface having the hardest wear but
on the bevel side of the surface.

The prolongation of rolling and rim wear reduces the effectiveness
of this method; also, it reduces the depth of the thermally processed
layer at some places all along the profile. Some areas with no thermally
processed metal layer on the wheel roll surface can appear after
grinding (see Fig. 3a).

There are no possibilities of increasing the thermally processed
metal layer of the wheel roll surface using this well-known method
because it is not allowable to reduce the gap between the inductor and
the roll surface by less than 3 mm. It is not possible to heat metal at
a temperature lower than 140[degrees]C because requirements for the
isothermal annealing-process mode, on which this method is based on,
would be violated.

This well-known method enables getting the abovementioned results
only when processing wheels where the layer of the roll surface does not
exceed 3 mm, whereas the established limiting value of the rolled layer
of the roll surface is 7 mm and that of the freight wagon - 9 mm. Taking
into consideration that the thermally-processed metal layer of 3/4 mm is
removed when repairing wheels with the help of the grinding method, it
is clear that an uneven thermally-processed metal layer of less than 5
mm remains or, in some places, is absent altogether. Even when the depth
of the thermally-processed metal layer is achieved using this method
processing the layer of the rolled metal and remains at its maximum, it
is, however, less than the required limit value, which means that the
thermally-processed layer will serve for the first stage of exploitation
only. The above-mentioned drawback is a typical one for the restoration
of the wheel profile using grinding, especially in the case of using it
while the working metal layer is shaved off. In addition, an increase in
hardness up to 320 HB before grinding reduces processing productivity
and the efficiency of the cutting mode as well as increases the
consumption of hard alloy, as compared with other above-mentioned
methods.

[FIGURE 3 OMITTED]

The aim of using this method is to improve the durability of the
wheel by preserving the rolling metal layer of the rim and by keeping
the depth of the thermally processed layer even when the hardness of
290+320 HB along the whole wheel roll surface is obtained.

This goal can be achieved by means of the abovementioned method for
restoring the profile of the wheel roll surface, according to which the
profile of the roll surface is restored employing the method of
high-speed profile grinding, which is the most efficient way of
preserving the rolling metal layer of the rim. Consequently, the wheel
roll surface is restored using thermal processing and ensuring an even
gap between the inductor and profile of the worn wheel roll surface.
This enables restoring physical and mechanical properties of the rim.

The use of the grinding method ensures an optimal gap between the
inductor and wheel roll surface along the length of the profile with the
rolling metal layer not being removed. An equal wheel size is guaranteed
before and after repair. The resistance of the metal layer of the wheel
roll surface to contact wear increases (see Fig. 3c) when the above
described processing method is applied. Wheel durability, in case of a
thicker layer, increases within exploitation.

5. Restoration and Experimentation on Exploitation

Restoration consists of the following stages: first, the wheel is
grinded to restore its worn and defective profile in accordance with the
given geometrical parameters; second, to ensure both even and maximum
hardness of the thermally-processed layer of 290+320 HB, an optimal 3 mm
gap between the inductor and wheel roll surface is set (see Fig. 3b).

By means of two half-coil inductors powered by one generator for
each wheelset, one for each wheel, the wheels are processed by
multi-pulse heating, chilling and cooling in the same way as in the
well-known method, which enables to get the structure of sorbitic
pearlite or sorbite of 290+320 HB hardness in an agreeable depth from
the roll surface evenly distributed along the length of the profile.

After such processing, the wheelset of the size as it was before
repair is further exploited and the hardness of its thermally-resistant
metal layer is 290+320 HB in depth which is equal to or even greater
than that required along the roll surface.

While trying to increase wheel durability by using this method,
differences appear when mechanical processing (grinding and polishing)
is made before annealing a multiplex impulse. To evaluate resistance to
both wear and other mechanical damages of the wheelset processed in
accordance with the suggested technology and to compare it with that of
typical wheelsets, experiments in exploitation were performed.

As an object to experimentation, thermally-processed wheels of 960
mm in diameter of RU-1 type were chosen (wagon service of Murmansk
station, Oktiabrskaja Railway, Russian Railways). The number of both
types of wheelsets was 8, and each wheelset was processed using
different methods. Those wheelsets were wheeled under the wagons of
model 10-4022.

[FIGURE 4 OMITTED]

Wagons having differently processed wheelsets were directed to the
circular route. The section (Apatites --Murmansk, Russia) is 185 km in
length and has 160 curves of 350/500 m radius. An average speed in this
section is 70 km/h and the general weight of the train is 8000 tons.

Difficult exploitation conditions in this section increase the wear
of wheelsets. The main reason for wheel rejection is the wear of the
wheel edge. Experimentation took place from April to May 2008.
Estimation criteria for the average run of the tested wagon making up to
400 km within 24 hours were chosen to be the degree of rim wear and the
wear of the wheelset roll surface, both depending on the mileage of the
wagon. The criteria were set by considering the prevailing samples and
other mechanical damages. The average wear of the wheelset at the end of
the experiment consisted of:

Based on the results of the conducted experiments, a Temporary
Technological Instruction on annealing the roll surface of wagon
wheelset together with Induction Heating and Thermo Cycling ([TEXT NOT
REPRODUCIBLE IN ASCII.] ... 2008) was drawn up.

6. Conclusions

1. The analysis of the obtained results has revealed that
experimental thermally processed wheelsets are more resistant to
abrasion than the typical ones. Experimental rims of the wheelset
exposed the strongest resistance to wear. No defects in those wheelsets
were found within the whole time of exploitation.

2. The presented method for restoring the profile of the wheelset
rim is based on high-speed profile grinding and aimed at obtaining,
after mechanical processing is performed, necessary physical and
mechanical properties of metal used for the wheelset rim considering
layer depth that exceeds the limit values of measured deteriorations.

3. The introduced method for restoring the profile of the wheelset
rim, by means of which the geometrical parameters of the roll surface of
the wheelset rim are regained with the subsequent restoration of
physical and mechanical properties of the surface layer of metal used
for the wheelset rim, enables strengthening the wheelset rim against
deterioration by about 30%.

[TEXT NOT REPRODUCIBLE IN ASCII] [Lysiuk, V. C. The reasons and the
mechanism of a wheel derailment. The problem of wheel and rail
deterioration]. [TEXT NOT REPRODUCIBLE IN ASCII], 188 c. (in Russian).